The present invention relates in general to telephone communication systems, and in particular to a digital loop carrier system based on a distributed architecture for cost effective and reliable provisioning of basic telephone services.
Existing telephone switch networks typically include a central office (CO) incorporating a group unit that connects to several line units (LUs). In a typical configuration the group unit provides the general cross-connect function and connects to each LU via 120 channels over four E1 links. Each LU supports between 700 to 1000 remote subscriber telephone lines. There are, therefore, from 700 to 1000 twisted-pair copper wires carrying telephone signals and connecting the telephones to each LU located at the CO. The traffic from the 700 to 1000 lines is concentrated onto 120 channels (i.e. 120 channels are shared among the 700 to 1000 lines) resulting in (acceptably low) probability of blocking. The central office connects to other similar central offices via trunks to facilitate telephone communication over a wider geographic area. These trunks are standardized in format. Commonly used standards are R2D and SS7.
In order to control the manufacture of subscriber switch access equipment, major switch manufacturers use a proprietary signaling system over the E1 links between each LU and group unit. Additionally, each switch manufacturer has developed a different interface standard. As a result, not only access to the telephone switching networks is severely limited, interfacing one type of equipment to several different switch types is expensive and complicated. To service large, newly developed areas, the user must either subscribe to an existing switch or a compatible switch attaching to the existing network must be purchased and installed.
In an area where the existing telephone network infrastructure is in place (such as the United States) the incremental cost of new hardware is relatively insignificant as compared to the extra support and maintenance costs associated with a different type of system. However, in those regions of the world where telephone lines are yet to reach large segments of the population, costs associated with obtaining and installing new CO switches, as well as the installation of copper twisted pairs over long distances for each subscriber can be a major barrier to extending service.
From the foregoing it can be appreciated that there is a need for a cost effective method of providing for basic telephone services where large numbers of newly added telephone lines are required.